Human fibroblast interferon production in poly(I) poly(C)-induced cultures of diploid human fibroblasts (FS-4 strain) is subject to a post-transcriptional (translational) repressor mechanism which appears to inactivate or degrade interferon mRNA. We are involved in the development of a coupled cell-free transcription-translation system in order to investigate the biochemical basis of this phenomenon. We propose to identify and characterize the two human fibroblast interferons that correspond to the l.3 and 0.9 kb mRNA species. We shall also investigate the functional stability of polyadenylated and deadenylated interferon mRNA species in homologous FS-4 cells.